1. Field of the Invention
This invention relates to the adaptation of a switching system using an exchange of the space switching type, to interconnect the lines of a communication network, each line being able to ensure the transmission of several communications in multiplex mode on respective channels which are different one from the others, the difference being possible either in the frequency domain, in the time domain or in any other way.
More particularly, this invention relates to such an adaptation when the nature of the communication does not involve a total independence of said communications, but, on the contrary, allows a common supervision of certain characteristics of the network, in particular a common definition of the channels in use. A particularly interesting example of such a case is given by the relations between peripheral units, also called "terminals", and one or several central units.
2. Description of the Prior Art
The problem relating to the interconnection of multiplex lines concerns the networks connecting terminals and central units as well as the telephone systems including multiplex lines for long distance calls.
In the present state of the technique concerning the central unit, terminal links, one has, on the one hand, the link of a central unit to several terminals with a common line and transmission in multiplex mode of messages on this line, and on the other hand, the link of one or several central units to terminals through a switching system, in which case, a single line ensures only one communication. The combination of the switching system and of multiplex lines does not appear.
A technique for switching multiplex lines through a space switching exchange is described in U.S. Pat. No. 3,652,803 which relates more particularly to the switching of multiplex telephone lines. In this case, the communications are independent and a common determination of the channels is very difficult. In that patent, the solution consists mainly in providing a channel register corresponding to each transmission channel of each line, and in interconnecting any one of the channel registers to another channel register through the exchange. This enables the link relating to a communication using channel x of a line and channel y of another line. Such a solution would be applicable should a common channel definition be possible, but it would not take any advantage of this additional condition.
The major difference between the present invention and the above identified patent lies in the fact that this invention does not use any channel register and that only the exchange control unit is adapted by the addition of an additional logic without modifying the exchange control logic itself. Among the advantages of this invention, the elimination of the registers corresponds to a real increase of the exchange capacity since only one input of the exchange corresponds to one multiplex line. Another advantage lies in the fact that any line can be connected to the exchange in the same way whether it is a multiplex line or an individual line, an individual line being a line providing only one communication as for example, a line connecting a subscriber's telephone set to an exchange. The exchange operation itself is also the same in both cases; accordingly, the exchange can be used simultaneously to inter-switch individual lines and multiplex lines, respectively.